| Color Models | |||||
| Describing Colors |
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| As mentioned in the Introduction
to Color page, a color
model is a technical standard for classifying colors. The two color
models most commonly used when designing for print are known as RGB
and CMYK.
RGB is typically used during the design process and CMYK is typically used during the print process, so knowing how they are different—or how to get them working together somehow—can help you aim for accurate color reproduction rather than be metaphorically blind, metaphorically, to the colors used in your design. Also, each way of describing color, each model, has limitations; the mixing of light or inks can only produce colors within a certain range, or "gamut". This is also known as a color space and is discussed further down this page after the two color models. If you have heard of and seen illustrations of these color models before, you can skip further down the page using the section links below: |
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| The RGB (Red/Green/Blue) Color
Model |
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 RGB is the color model used for devices that create
colors using light e.g. monitors. It is based on the fact that you
can make any color from the spectrum by combining different intensities
of the three primary colors (red/green/blue). Of course, a monitor
can’t reproduce every color in nature—that’s where
the concept of gamut or color space comes in (see below). However,
we can describe any color that does fall within the limited RGB color
space using three numbers from 0 to 255, representing the proportions
of the primary red, green, and blue constituents.
The RGB color model is called an additive model, which relates
to the fact that we’re perceiving color as a mixture of discrete
wavelengths of light transmitted directly from several sources—for
example, from the red, green, and blue phosphors in a monitor screen.
Each source adds its contribution to the mix, ultimately (when 100%
R, G, and B wavelengths are mixed) producing white light as shown
in the diagram. |
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| The CMYK (Cyan/Magenta/Yellow/Black)
Color Model |
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 CMYK is the color model used for devices like printers
that create colors using inks, pigments, or dyes. It is an enhancement
on the basic CMY model which uses just the three “subtractive” primary
colors (see diagram). In theory, if all the CMY inks are present at
full intensity, the result should be pure black. But, in practice
because of the impurity and transparency of the inks, a dark gray
color is produced instead. Black (denoted by the letter K in CMYK)
is included to ensure the clarity of the darker tones. CMYK describes
any color by assigning a value (zero to 100%) to each of the proportions
of the four ink color constituents.
This color model is called subtractive because in this case what
we perceive as color starts out as a more-or-less white light source
(say, a desk lamp) reflecting off a pigment that subtracts certain
wavelengths. A red ink only reflects red wavelengths; it subtracts
(or absorbs) the rest. The more ink or pigment colors you mix, the
closer you approach something we call black because more light is
absorbed by the ink. |
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| Gamut and Color Space - Color
Ranges |
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Of course, the “black” obtained from mixing inks (or showing a dark computer screen) is hardly the same black you’d experience in a dark room or cave. Remember that color includes not just hue, but also light versus dark and intensity versus paleness. No technology can come close to matching the human eye’s range or gamut of vision. Each color model has its own comparatively limited gamut or color space. The diagram below shows in a very schematic way how various color spaces compare with each other, within the overall range of colors we can typically see. Even the best photographic film (see “Wide RGB” gamut, below) can capture only a portion of the color range discernable to the human eye. The important thing to bear in mind for professional printing is that an RGB monitor has a far smaller gamut than film, and a printer using CMYK can reproduce even less.
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| What This Means to Us as Designers |
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| Desktop publishing programs like Serif PagePlus allow you to specify colors in your design in
terms of their CMYK ink components, and although
the monitor still shows us these colors using
red green and blue light, the program's PDF-output
file will know about and maintain your use
of CMYK color definitions and in turn they are
recognized by the professional offset and most
laser print processes. This allows you to plan
your color usage, knowing that your color choices
will be respected by the design program, the
transferable output file, and the print process.
Avoid “out of gamut” bright RGB colors in your design
to avoid disappointment with your printed results
and be prepared to expend a little effort making
sure your design elements will emerge
looking their best on the printed page.
Having mentioned that you can specify CMYK colors in good publishing
software, yet knowing that they are still represented by red, green,
and blue light from your monitor, there is another bridge to cross.
How do we know what our carefully-chosen CMYK design colors, which
are represented on our monitor by RGB light wavelengths, will actually
look like when printed with CMYK inks? There are some techniques
that can help us better manage the differences between screen colors
and printed colors—learn more in the next section, color
management. |
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